In radio telephone systems, for example in the CD500 GSM (Group Speciale Mobile) terminal (i.e. radio telephone), the required clock accuracy is 0.1-0.5 ppm (parts per million). A typical prior art radio telephone system which has such a clock accuracy is described with reference to the accompanying FIG. 1.
FIG. 1 describes a prior art solution for accurate time measurement. The solution involves a fast clock oscillator 1 and a counter 2. The fast clock oscillator 1 is in use continuously and the oscillator pulses are measured by the counter 2. To reach the required accuracy it is required to have an Automatic Frequency Control (AFC) function based on the reference of the signal transmitted by the system (i.e. transmitted by the base station).
Both the clock oscillator 1 and the counter 2 consume a considerable amount of current at high frequencies.